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Precious metals have been shown to play a vital role in the selective hydrogenation of α,β-unsaturated aldehydes, but still suffer from challenges to control selectivity. Herein, we have advanced the design of catalysts made out of Pt–Co intermetallic nanoparticles (IMNs) supported on a MIL-101(Cr) MOF (3%Pt y %Co/MIL-101(Cr)), prepared by using a polyol reduction method, as an effective approach to enhance selectivity toward the production of α,β-unsaturated alcohol, the desired product. XRD, N 2 adsorption–desorption, FTIR spectroscopy, SEM, TEM, XPS, CO adsorption, NH 3 -TPD, XANES and EXAFS measurements were used to investigate the structure and surface properties of our 3%Pt y %Co/MIL-101(Cr) catalysts. It was found that the Co-modified 3%Pt y %Co/MIL-101(Cr) catalysts can indeed improve the hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL), reaching a higher selectivity under mild conditions than the monometallic Pt/MIL-101(Cr) catalysts: 95% conversion of CAL with 91% selectivity to COL can be reached with 3%Pt3%Co/MIL-101(Cr). Additionally, high conversion of furfural (97%) along with high selectivity to furfural alcohol (94%) was also attained with the 3%Pt3%Co/MIL-101(Cr) catalyst. The enhanced activity and selectivity toward the unsaturated alcohols are attributed to the electronic and geometric effects derived from the partial charge transfer between Co and Pt through the formation of uniformly dispersed Pt–Co IMNs. Moreover, various characterization results revealed that the addition of Co to the IMPs can promote the Lewis acid sites that facilitate the polarization of the charge-rich CO bonds and their adsorption via their oxygen atom, and also generate new interfacial acid sites.
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Local reactivity descriptors to decipher the electrochemical hydrogenation of unsaturated carboxylic acids
The decarbonization of chemical manufacturing is a multifaceted challenge that requires technologies able to selectively convert CO2-sequestering feedstocks using renewable energy. The electrochemical conversion of biomass-derived platform chemicals is well-positioned to address this need. However, the electroactivity of biobased molecules that carry multiple redox centers remains challenging to predict and control. For instance, cis,cis-muconic acid, a conjugated dicarboxylic acid, is electrohydrogenated to trans-3-hexenedioic acid (t3HDA) with excellent yield and stereoselectivity while free energy calculations predict mixtures of 2- and 3-hexenedioic acids. To decipher this discrepancy, we studied the electrohydrogenation of C4 and C6 unsaturated acids, diacids, and their esters, and tied the observed product distributions to the electronic structure of the parent molecules. We show that the electrohydrogenation of the three isomers of muconic acid proceeds through a hydrogenating proton-coupled electron transfer (PCET) in the α position of the carboxylic acids and invariably yields t3HDA as the sole product. The selectivity can be explained by the electron-withdrawing effect of the carboxylic acid groups and the resulting perturbation of the local electron density that promotes the 2,5-hydrogenation over the thermodynamically-preferred 2,3-hydrogenation. This electronic perturbation is reflected in the computed Fukui indices, which can serve as local reactivity descriptors to predict product distributions not captured by calculated reaction thermochemistry. In addition to predicting the electroactivity of other unsaturated acids, this approach can provide insights into homogeneous electrochemical processes that may coexist with surface-mediated electrocatalytic transformations.
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- Award ID(s):
- 2132200
- PAR ID:
- 10539294
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 25
- Issue:
- 24
- ISSN:
- 1463-9262
- Page Range / eLocation ID:
- 10387 to 10397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D3GC02909C
